1. Field of the Invention
This invention relates to an acrylonitrile maleimides solution composition of improved shelf life and a method for the production thereof.
2. Description of the Prior Art
Maleimides are compounds useful as raw materials for synthetic resins, medicines, and agricultural pesticides. The maleimides which are solid at normal room temperature have been heretofore handled generally in various forms such as powder, flakes, and tablets. The maleimides in these forms contain minute particles of maleimides. While these maleimides in solid state are in transit, they undergo gradual comminution and give rise to minute particles of maleimides in a large amount.
The maleimides have undersirable qualities. They in themselves give a stimulus to human bodies. Particularly when their minute particles are inhaled, they stimulate the nasal cavities and the throats and incite coughs and sneezes. When their minute particles are suffered to adhere to the skins and remain there, they cause inflammation of the skins. When a person happens to handle maleimides containing such minute particles, he is required to take elaborate precautions to keep his skin from the maleimides.
In the circumstances, immense labor is expended for preventing the maleimides from shedding minute particles during the course of transportation or for removing minute particles from the maleimides after the transportation.
In most cases, solid substances are transportated as stowed in paper bags, drums and containers. Persons engaging in any part of the work involved herein are inevitably exposed to the maleimides, with the natural result that minute particles of the maleimides adhere to their bodies.
At attempt at conveying solid substances by a pipeline for the purpose of precluding the solid substances from contacting human bodies is basically difficult. The solid substances in transit through the pipeline are apt to clog the interior of the pipeline. For the solid substances to be stably conveyed by the pipeline, harsh restrictions are imposed on the shape, size, specific gravity, etc. of the solid substances to be conveyed.
It is only safe to conclude that methods employed for transportation or conveyance of maleimides which are solid at room temperature entails various difficult problem. Similar problems are also encountered by methods to be employed for storage of the maleimides.
A method for conveying, transporting, or storing maleimides as a solution in acrylonitrile has been disclosed in Japanese Patent Laid-Open SHO 62(1987)-126,167. This method may well be called highly satisfactory in the sense that it can solve the problems mentioned above in the handling of maleimides.
The acrylonitrile maleimides solution in common use manifests heavy corrosiveness to metals. The phenomenon that such materials as carbon steel and stainless steel which are popularly used in industries are rapidly corroded by the acrylonitrile maleimides solution is observed frequently.
Moreover, this solution in storage generates an insoluble component therein tarnishes wholly in a blackish tint. This phenomenon of tarnishing entails a disadvantage that the maleimides are appreciably degenerated and consequently deprived of commercial value.
The desirability of developing an acrylonitrile maleimide solution relieved of heavy corrosiveness and improved in stability has been finding enthusiastic approval in the industry.
As one way of producing the acrylonitrile maleimides solution, there may be cited a method which comprises preparing a tank provided with a heating coil or a heating jacket and a stirrer, filling the tank with acrylonitrile to capacity, adding solid maleimides in the form of flakes, granules, or particles to the acrylonitrile, and then heating the resultant mixture by means of the heating coil or the heating jacket thereby dissolving the maleimides thoroughly in the acrylonitrile.
The solid maleimides assume various forms such as flakes, tablets, granules, and minute particles as described above. Without maleimides possess a quality such that, while the solid maleimides are in storage, their individual particles coalesce and form very hard lumps.
These solid maleimides are generally stored as stowed in paper bags, plastic bags, drums, and containers. During their storage, however, they are transformed into large hard lumps owing to the aforementioned quality peculiar to the solid maleimides.
When such lumps of solid maleimides are to be dissolved in acrylonitrile, these lumps in process of conveyance from their containers to a maleimides dissolving tank (hereinafter referred to simply as "dissolving tank") are suffered to clog a nozzle for injection of the solid maleimides into the dissolving tank and consequently disrupt the operation of dissolution.
Further, the dissolution of the solid maleimides in acrylonitrile proceeds with large absorption of heat and, therefore, requires the contents of the dissolving tank to be heated to ensure safe dissolution.
The inevitable formation of such large, lumps obstructs effective control of the introduction of the solid maleimides into the dissolving tank. When the feed rate of the solid maleimides into the dissolving tank is unduly lowered, the liquid temperature inside the dissolving tank is heavily fluctuated.
Owing to this heavy fluctuation of the inner temperature of the dissolving tank, the acrylonitrile maleimides solution once formed is compelled to induce precipitation of crystals of maleimides in a large volume. When the lumps of maleimides happen to enter the dissolving tank in a large amount at once, the heat imparted to the solution by the heating falls short of reaching the level required for dissolving the maleimides, with the result that the lumps of solid maleimides remain intact within the dissolving tank.
When this situation arises, the dissolving tank is no longer capable of continuing the operation of stirring which is indispensable to the work of dissolution. Then, the lumps cannot be dissolved. There are times when the failure of the dissolving tank to stir the inner liquid thereof entails local heating of the part of the inner liquid approximating to the surface of heating and brings about serious consequences such as, for example, polymerization of the solution.
The operation of dissolution under discussion is generally carried out at a high temperature close to the boiling point of acrylonitrile. As widely known, acrylonitrile is an extremely flammable compound and the acrylonitrile vapor, on mixture with the air, readily produces an explosive gas.
As mentioned above, the solid maleimides are stowed in returnable containers, drums, paper bags, and plastic bags. These containers do not easily permit thorough displacement of the air entrapped therein with an inert gas. When the solid maleimides are released from such containers as mentioned above and introduced into the dissolving tank to be dissolved in acrylonitrile therein, the air existing in the gaps between the individual particles of the solid maleimides is inevitably entrained by the solid maleimides and allowed to mingle with acrylonitrile and give rise to the explosive gas.
The existing methods available for the dissolution of solid maleimides in acrylonitrile do not deserve to be called perfect in the strict sense of the word.
The circumstances quite aptly urge the development of a method which produces an acrylonitrile maleimides solution without entailing any of the drawbacks mentioned above.
An object of this invention, therefore, is to provide an acrylonitrile maleimides solution of improved shelf life and a method for the production thereof.
Another object of this invention is to provide a method for producing an acrylonitrile maleimides solution easily without exposing human bodies to minutes particles of maleimides.
A further object of this invention is to provide a method for producing an acrylonitrile maleimides solution even from solid maleimides which have coalesced by change into coarse lumps during storage.